The invention relates to a whole machine mounting device for a wind turbine, which is used for offshore wind power generation. The whole machine mounting device comprises an underframe (1), a support (2), a jacking device (4) and buffer plates (6), wherein the underframe (1) is of a conical semi-round table structure with split type assembly, the support (2) is of the shape of a pyramid, the bottom of the support (2) is of a vertex of the pyramid, the jacking device (4) is arranged in the center position on the support (2), and the jacking device (4) can ascend or descend along the vertical direction in the middle position of the support (2); a precision positioning device (5) is arranged on the support (2) and comprises drivers (51, 52) and a positioning hole seat (53), and a positioning hole (54) is formed on the positioning hole seat (53); and the buffer plates (6) are arranged at the two ends on the outer side of the upper surface of the support (2). The device disclosed by the invention has the characteristics of smoothness in offshore mounting, capability of realizing whole machine mounting of the wind turbine, and time-saving and labor-saving properties in mounting.